Copyright Goodheart-Willcox Co., Inc. 126 Section 2 Fundamentals of Shape Description Conventional Practice in Section Views Section views present many opportunities for con- ventional practice. A conventional practice is one in which drafters break the principles or rules of projec- tion theory for the sake of clarity. Standards establish the rules for a particular exception. One example of a conventional practice can be called the “rib rule.” Many sectioned objects have thin walls, webs, or ribs that help support a feature of the object, as in Figure 6‑11. To avoid a false impression of thickness, it is a conventional practice to leave the web or rib without section lines. Also, the rib is outlined, even though the cutting plane passes through it. This rule applies when the cutting plane is parallel to the thin material, not when the cutting plane passes across it in a perpendicular fashion. In some cases, it may be clearer to show the rib or web sectioned with alternating lines to distinguish it from the rest of the sectioned area. The aligned section illustrated in Figure 6‑12 also shows the conventional practice for spokes of a wheel. As with the rib rule, spokes and arms in a section view are not section lined, because it would give the impression there is a solid web. Other Section View Practices There are a few other practices specific to section views that should be explained in this unit. A section can be a partial section. This practice allows for a removed section to show details of an object without drawing complete views. In Figure 6‑13, the partial Goodheart-Willcox Publisher Figure 6‑11. It is conventional practice to leave webs or ribs without section lines. Rib is cut, but section lines are not shown Showing section lines gives a false impression of thickness Avoid Conventional Practice Alternate Practice (2X Scale on Rib) Goodheart-Willcox Publisher Figure 6‑12. It is conventional practice to leave spokes without section lines. Goodheart-Willcox Publisher Figure 6‑13. A partial section view shows details of an object without drawing complete views.